An example of a molten metal container such as tundish or ladle is shown in FIG. 14. A tap hole 4 is formed in a nozzle seating block 3 at the bottom 2 of a tundish 1 as a molten metal container. An insert nozzle 5 is inserted through the tap hole 4 into the tundish 1. A lower part of the insert nozzle 5 is supported on the top surface of the periphery of a hole 8 of a bottom plate 7 of a slide valve device (hereinafter referred to as the SV device) 6 mounted on the underside of the tundish 1. At a lower part of the SV device 6, an upper part of a submerged nozzle 9 is held in a suspended manner by a submerged nozzle support device 11 via a nozzle case 10.
In continuous casting equipment, as shown in FIG. 15, a lower part of the submerged nozzle 9 is immersed in molten metal 13 contained in a mold 12 of a water-cooled structure. Through outlets 9a formed at the periphery of the lower part of the submerged nozzle 9, molten metal 13 is continuously poured into the mold 12. Molten metal 13 cooled at the peripheral surface in the mold 12 gradually solidifies. During this period, the molten metal 13 is discharged from the bottom to be guided to a next step.
The SV device 6 operates in the following manner: A slide plate 16 is connected to a piston rod 15 of a hydraulic cylinder 14 so as to slide in a horizontal direction. When the hydraulic cylinder 14 is actuated, the slide plate 16 slides to bring a hole 17 of the slide plate 16 into or out of alignment with the hole 8 of the bottom plate 7. As a result, the amount of molten metal outflow is controlled.
The submerged nozzle 9 has a somewhat increased-diameter upper end, which is fitted into the nozzle case 10. The upper end face of the submerged nozzle 9 is pressed against the lower end face of a chute nozzle 18 via a seal packing (not shown). On the outer surface of the nozzle case 10, support pins 19, 19 protrude at diametrically symmetrical positions.
As described above, the lower portion of the submerged nozzle 9 is always immersed in a molten metal and washed thereby. Since it is thus damaged and worn, it should be replaced, where necessary, by a fresh submerged nozzle 9.
Under these circumstances, the submerged nozzle support device 11 has been used which can rapidly replace the submerged nozzle 9. In the conventional example of FIG. 14, an air cylinder 21 with a downwardly facing piston rod 20 is provided on the underside of the SV device 6. To the piston rod 20 of the air cylinder 21, a support arm 22 is secured. On the distal end of the support arm 22, recesses 23 are provided so that the submerged nozzle 9 is held in a suspended state by the support pins 19, 19 of the nozzle case 10. Into the recesses 23, the support pins 19, 19 of the nozzle case 10 are fitted, and then the air cylinder 21 is contracted. Thereby, the upper end face of the submerged nozzle 9 is pressed against the lower face of the periphery of the hole 17 of the slide plate 16 of the SV device 6, or if the SV device 6 is provided with the chute nozzle 18, it is pressed against the lower surface of the chute nozzle 18 via the seal packing. By this measure, the submerged nozzle 9 is fixed. The fixing means may employ a lever system or a toggle mechanism.
In replacing the submerged nozzle 9, however, the above-described device requires the following procedure: The slide plate 16 of the SV device 6 is caused to slide until its hole 17 is closed. The tundish 1 is raised, and then the air cylinder 21 is extended to lower the support arm 22. The submerged nozzle 9 is then removed manually, and the underside of the chute nozzle 18 is cleaned. Then, a fresh submerged nozzle 9 and a seal packing are set. Thereafter, the air cylinder 21 is contracted to lift the submerged nozzle 9, and the tundish 1 is lowered simultaneously. The slide plate 16 of the SV device 6 is caused to slide until its hole 17 is opened.
This replacement work takes 60 to 90 seconds at the earliest, thus posing a major problem: During this replacement of submerged nozzle 9, the surface of the molten metal 13 in the mold 12 solidifies, and the seams of the molten metal 13 are reduced to scrap. Consequently, the yield drops.
It may be attempted to shorten the time during which the withdrawal of the molten metal 13 is interrupted. However, the submerged nozzle 9 after use must be detached, and a fresh submerged nozzle 9 set. Thus, there are limits to shortening the time. One may try not to move the tundish 1 up and down, but to cut the time required for this upward and downward movement. However, the presence of the SV device 6 makes the space below the tundish 1 narrow. Replacement work within this narrow space is very laborious, making rapid replacement difficult.
Furthermore, the replacement work is done manually. The submerged nozzle itself is made of refractory, so that it is heavy and its mounting and dismounting are not easy. The surroundings of the SV device 6 are at extremely high temperatures. The work must be done under hot conditions, meaning an adverse work environment. From this aspect as well, the work is intractable.
Technologies for further facilitating replacement work for the submerged nozzle are described in Japanese Laid-Open Patent Publication Nos. 292955/94 and 52760/91. These techniques use a running trolley, and place a handling device on the trolley. The trolley is moved to a predetermined position to hold the submerged nozzle, so that the submerged nozzle is mounted at the bottom of the SV device. The apparatus used is itself grandly structured, and costs heavily. A wide space must be secured for its movement. In addition, the handling device is actuated after the trolley is moved to the position of submerged nozzle replacement. Thus, the operation of the apparatus is so slow that the replacement of the submerged nozzle takes time. These earlier technologies are unable to solve the aforementioned problems completely.
An object of the present invention is to provide a submerged nozzle replacing device which can rapidly perform replacement work for a submerged nozzle, eliminate the casting interruption time, and dissolve the scrapping that occurs at the seams of molten metal.
Another object of the invention is to provide a submerged nozzle replacing device which enables the setting of a fresh submerged nozzle, its mounting on the SV Device, and the withdrawal of the used submerged nozzle to be performed by a single guide efficiently and less laboriously.